An equivalent time sampling oscilloscope (hereinafter referred to as a sampling oscilloscope) is conventionally known as, for example, a sampling oscilloscope that repeatedly samples a signal to be measured from an object to be measured (DUT) such as a high-speed transceiver or an optical fiber connection module (SFP+) and displays an observed waveform or an eye diagram. For example, a sampling oscilloscope disclosed in Patent Document 1 generates a periodic signal of which the frequency is slightly shifted from a frequency of 1/integer of a reference clock signal using a direct digital synthesizer (DDS) and performs sampling of a signal to be measured using this generated periodic signal as a time base.